In recent years substrate surfaces with periodic or quasi-periodic nanostructures have found widespread use in a broad range of different applications, e.g. in the fields of optics, electronics, spectroscopy, sensor technology, lithography etc.
Especially advantageous methods for generating such nanostructures involve the use of self-assembling techniques such as block copolymer micellar nanolithography (BCML) and similar methods. In comparison with “classic” lithographic processes, self-assembling techniques are relatively simple, inexpensive, very fast and are principally suitable to provide even rather extended or 3-dimensional surfaces with the desired nanostructures.
However, in contrast to conventional lithographic methods such self-assembling techniques are more prone to the generation of structural defects. It is possible to minimize the presence of such defects by selecting suitable process conditions but it is difficult to avoid such inherent defects completely. Moreover, the interparticle distances of such structures tend to vary to a certain extent. Both structural defects and variations of the interparticle distance are very undesirable for many applications. This limits the use of self-assembling techniques for structuring surfaces in spite of the above advantages.
It is known to heal structural defects of 3-dimensional crystals by thermal annealing processes. In the course of such annealing processes, the thermal energy applied to the crystalline system results in the generation of an excited state of the system which can be re-structured and re-ordered rather easily, leading to the elimination of structural defects. The corresponding increase of the crystal lattice order obtained by these processes is largely maintained when the crystalline system returns into the ground state.
Attempts have been made to improve the degree of order of self-assembled nanostructures on a substrate surface by annealing processes as well. For this purpose, processes based on either vapour annealing (Yoo et al., J. Mater. Chem. 2007, 17, 2969-2975) or solvent annealing (Cavicchi et al., Polymer, 46, 2005, 11635-11639) were developed. The method of vapour annealing involves exposing the nanostructured substrate for several hours to an atmosphere of a specific solvent, such as THF. This method is slow and requires a rather sophisticated equipment and the use of toxic solvents. In the method of solvent annealing a thin solvent film is applied onto the substrate and subsequently evaporated in a controlled manner in a suitable atmosphere such as nitrogen. This method is only applicable for some polymers and is also quite laborious due to the required controlled evaporation. Moreover, both methods are often not suitable to achieve a very high degree of order of the nanostructures.
Thus, an object of the present invention is to provide improved methods for producing highly ordered arrays of micelles or nanoparticles on a substrate which are fast, cost-efficient and simple to perform without the need of expensive equipment.
A further object is to provide large and very highly ordered arrays of micelles or nanoparticles on a substrate surface.
Said objects are achieved according to the present invention by providing novel methods for producing highly ordered arrays of micelles or nanoparticles on a substrate which involve an annealing step by ultrasonication in a polar liquid medium and by providing the highly ordered array of micelles or nanoparticles according to the invention.